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dexar [7]
3 years ago
10

A customer works into a post office to purchase stamps. she purchases a total of 45 stamps. some of the stamps are 49cent stamps

and some are 33cents stamps. how many 49cent stamps and how many 33cent stamps did she purchase if the total cost of all the stamps was $17.89
Mathematics
1 answer:
baherus [9]3 years ago
5 0

Step-by-step explanation:Let number of 49 cents =A

                                             Let number of 33 cents=B

<u>A+B=45    equation 1</u>

1 $=100 cents

49 cents =.49 dollar

33 cents=.33 dollar

so .<u>49A+.33B=17.89    equation 2</u>

Add equation 1 and equation 2

since these are simultaneous equations

.49A+.33B=17.89

     A+     B=45

so divide equation 2 by 100 we get

49A+33B=1789

    A+B     =45 multiply equation 1 by 33 on both the sides we get

<u>33A+33B=1485     equation 3</u>

so subtract equation 3 from equation 2 we get

49A+33B=1789  equation 2

<u>33A+33B=1485    equation 3</u>

<u>16A+0      =304</u>

16A=304

A=304/16

A=19

putting nalue of A in equation 1 we get

A+B=45

19+B=45

B=45-19

B=26

so number of 49 cent stamps are 19

and number of 33 cent stamps are 26

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Answer:

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And the correct interpretation for this case is:

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Step-by-step explanation:

Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % where by a population means lies between an upper and lower interval".  

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Solution to the problem

The confidence interval for the mean is given by the following formula:  

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In order to calculate the critical value t_{\alpha/2} we need to find first the degrees of freedom, given by:  

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Since the Confidence is 0.95 or 95%, the value of \alpha=0.05 and \alpha/2 =0.025, and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-T.INV(0.025,24)".And we see that t_{\alpha/2}=2.06  

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The 95% confidence interval would be given by (122;138)

And the correct interpretation for this case is:

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